1. Technical Field
The present invention relates to an improved product conveyor apparatus and, in particular, to a product conveyor apparatus which provides for efficient dispensation of the product on the first run through the product conveyor by use of a stopper gate. A plurality of stopper gates are positioned adjacent to a plurality of slide doors in the bottom of the product conveyor and controlled in order to limit the amount of product that is recycled along the recirculation conveyor. The invention greatly reduces the potential for product staling due to excessive product recirculation.
2. Description of Related Art
A vibrating conveyor is a commonly used device in the food industry for dispensing products such as potato chips into weighers. In most packaging lines, a product is moved along vibrating distribution conveyors having multiple product weighers placed below and along the length of the conveyor. When a weigher requires product, a slide door opens in the bottom of the distribution conveyor over that particular weigher and drops product onto the weigher. It is possible that the product might pass over all of the weighers without being dropped because none of the weigher doors are open when the product passes over. Rather than simply discarding the product that was not dispensed into the weighers, a recirculation conveyor is typically used to re-route the undispensed product back to the beginning of the distribution conveyor.
An example of a prior art design in this regard is illustrated by FIG. 1A. Throughout the specification, the same numerals are used to denote like parts. FIG. 1A shows a top view of a distribution conveyor 100 with a plurality of slide doors 105 and a recirculation conveyor The distribution conveyor 100 consists of multiple sections of distribution conveyor pans (not shown), each having a plurality of slide doors 105 mounted in the bottom of the conveyor pan. The conveyor pans are vibrated in the direction of product flow 125. In operation, the pan drops downward and in the opposite direction of product flow, and then lifts upward and forward in the direction of product flow 125. In this manner, the product is moved to a higher elevation at the end of each distribution conveyor pan before it is dumped onto the next distribution conveyor pan at a lower elevation.
The slide doors 105 are controlled by a weigher underneath the door 105 which sends a signal to open the slide door 105 when more product is needed. Thus, each slide door 105 operates independently of the other slide doors 105. The recirculation conveyor pans are similar in operation to the distribution conveyor pans except that they do not have slide doors, operating simply to move the product back to the initial stage 120 of the distribution pan.
FIG. 2A shows the distribution conveyor 100 in operation. The product 200, such as potato chips, comes out of the kitchen and is deposited onto the initial stage 120 of the distribution conveyor 100. It then passes over multiple slide doors 105 until it is dropped into an open slide door 105. If it passes over all of the slide doors without being dropped, then it is deposited onto the upstream end 130 of the recirculation conveyor 115 and re-routed back to the initial stage 120 of the distribution conveyor 100. In a typical system, approximately 20% of the product is re-routed down the recirculation conveyor back to the distribution conveyor. A significant portion of this 20% will get re-routed a second or third time. It is conceivable that some portion of the product will never get dropped during a given product distribution run.
The longer the product remains on the conveyor, the more it cools and, consequently, the ore moisture that is absorbed by the product. As the product is circulated from the distribution conveyor 100 to the recirculation conveyor 115 and back to the distribution conveyor 100, it will decrease in temperature to the point that the vapor pressure of the product is exceeded by the surrounding atmosphere. When this happens, the product absorbs moisture from the atmosphere, increasing its moisture content. Excess moisture in a packaged product can lead to premature staling. The shelf life of the packaged product is therefore reduced when the product makes a subsequent pass on the distribution conveyor 100. Furthermore, even if only a portion of the product packaged in a bag bad been recirculated, the absorbed moisture of the recirculated product would also affect the product that had not absorbed any moisture, causing it to go stale faster as well.
Environmental conditions of the room can be controlled by increasing the temperature and decreasing the humidity. This is not a feasible solution because the equipment needed to control the environment in the room is extremely expensive to purchase, operate, and maintain. Another alternative is to keep the product warmer by using infrared heaters placed above the product. Using this method to keep the product warm, the product could theoretically be circulated for hours at higher than room temperature without absorbing moisture from the ambient air. However, the obvious shortcoming of this solution is that it would require an electrical or gas energy source. This added energy cost decreases the profitability of the operation and makes it a much less attractive solution. Further, maintaining the product at an elevated temperature for an extended period of time could affect the characteristics and quality of the product.
Thus, the best solution is to develop a method and apparatus for dispensing the product into the weighing mechanism as soon as possible after it enters the packaging line, preferably on the first pass of the product through the distribution conveyor. When packaged in this manner, the product does not have time to cool down and absorb moisture from the ambient air before it is packaged in a vapor-proof bag.